INSPECTION TECHNOLOGY
technology; the other employs an acoustic emission monitoring system.
In the Thermoflight research project, Fraunhofer
scientists are working together with industrial and research partners to investigate alternative inspection methods. As we reported in April 2017, offshore drones equipped with thermal imaging cameras in combination with acoustic monitoring systems could potentially improve maintenance efficiency and help reduce downtime. The acoustic emission measuring system integrated
in the rotor blade serves as an early warning system by detecting internal damage, for example at the root of the rotor blade. The thermal imaging camera, on the other hand, detects surface damage, such as that caused by rain erosion. Fraunhofer IWES is optimising the non-destructive
acoustic emission monitoring system for the inspection of rotor blades. Acoustic emission and piezoelectric sensors are attached to the inner surface of the rotor blades in structurally relevant areas – especially at known weak points. The measurement computing device that collects and analyses the sensor data is integrated in the rotor hub. “The sensors work in much the same way as
microphones,” explains project manager Stefan Krause. “If the tensile forces in a specific area of the rotor blade suddenly change, the structure releases energy in the form of heat and surface waves that can be measured by the sensors. The sound waves captured by each sensor have different signal delays. By analysing their arrival times, it is possible to pinpoint the source of the damage.” The acoustic emission measuring system has
already delivered convincing results during lab tests in the institute’s rotor blade testbed facility. During static rotor blade and fatigue tests, the researchers were able to identify numerous types of damage, including adhesive and inter-fibre fractures, damage to web-flange joints, cracks in the trailing edge of rotor blades, and faulty bonding in the blade root area. The next step is to test the system under real-life conditions. These tests will be carried out in this spring in the Meerwind Süd and Meerwind Ost wind parks off the coast of Helgoland, northern Germany.
LARGE ROTOR BLADE ASSEMBLIES The acoustic emission measuring system is an efficient and reliable means of continuously monitoring very large structures. As soon as the sensors detect and localise a potential defect, appropriate measures can be initiated. Depending on the type of damage and its location, a closer, external inspection of the rotor blade could, for example, be carried out using a thermal imaging camera. Structural defects cause friction which in turn
generates heat. The heat flow in the material can be detected by means of thermal imaging. In this project, a passive thermography technique is employed in which heat flow measurements are based on the intrinsic heat of the object under test or on differences in temperature due to the natural diurnal cycle. Deutsche WindGuard Engineering and BIMAQ have been successfully applying thermal
42 /// Environmental Engineering /// March 2018
❱❱ Manual inspection of rotor blades at off-shore wind farms is hampered by weather, with climbing teams often having to stand down at short notice as conditions change, making planning difficult and costly
surveying to visualise heat flow in operating onshore wind farms for several years. The new challenge is to adapt this proven technique to the requirements of offshore installations. By attaching thermal imaging cameras to drones, it
is possible to detect subsurface defects in composite materials, including delamination, inclusions, faulty bonding in the loadbearing web-flange joints, and shrinkage cavities. Under operational load, such defects deep inside the rotor blade, if not detected and dealt with in good time, can provoke more serious structural damage and eventually lead to a total breakdown. “Our aim is to combine different test methods so that such damage is detected sooner, thus avoiding the need for emergency shutdowns. It also allows operators to carry out targeted rotor blade inspections,” says Nicholas Balaresque, CEO at Deutsche WindGuard Engineering. The company has successfully completed initial lab
tests of the thermography system. The next step is to choose the camera system and type of drone. As part of the tests to validate the concept of using thermal imaging for the structural health monitoring of rotor blades, evaluation algorithms are being developed on the basis of additional measurements being carried out at the University of Bremen’s wind energy research facility. To complement this work, offshore wind park operator WindMW Service is designing application scenarios for rotor blade inspections with the aim of sustainably reducing and optimising the number of regular inspections.
REDUCING COSTS AT SEA As well as reducing inspection costs, the new combined method promises to increase energy yields by reducing downtimes. An industrial climber needs a whole day to inspect a rotor. “Using drones, the same work could be done within one hour,” Krause estimates. “And a targeted inspection based on the results of acoustic emission measurements would require even less time. “These new technologies, particularly in
❱❱ To read more on inspection technology, scan the QR code or visit
http://goo.gl/Qq9bBr
conjunction with unmanned aerial vehicles (UAVs), complement traditional inspection activities by offering an efficient, safe means of inspecting rotor blades with optimised use of resources and minimum disruption of energy production.” EE
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52